Vista Home Premium and networking many XPs to a Vista Share

I have a Vista Home Premium machine sharing a folder....not the "Public"
folder within Vista...let's call it Public2. For a full week all the
machines could access the share with no issues....note: it is wide open
using "guest access"

One night I installed Symantec antivirus corporate client v10.2, and now the
users experience constant intermittent drops from the share. They can open a
microsoft word file off the share and work the file...when they save it, the
shared is no longer accessible.

I have verified that the LAN connection is constantly up---no sleep mode and
can not seem to figure out the problem. Any ideas?